Dynamically generated baryon resonances

Identifying a zero-range exchange of vector mesons as the driving force for the s-wave scattering of pseudo-scalar mesons off the baryon ground states, a rich spectrum of molecules is formed. We argue that chiral symmetry and large-$N_c$ considerations determine that part of the interaction which generates the spectrum. We suggest the existence of strongly bound crypto-exotic baryons, which contain a charm-anti-charm pair. Such states are narrow since they can decay only via OZI-violating processes. A narrow nucleon resonance is found at mass 3.52 GeV. It is a coupled-channel bound state of the $(\eta_c N), (\bar D \Sigma_c)$ system, which decays dominantly into the $(\eta' N)$ channel. Furthermore two isospin singlet hyperon states at mass 3.23 GeV and 3.58 GeV are observed as a consequence of coupled-channel interactions of the $(\bar D_s \Lambda_c), (\bar D \Xi_c)$ and $(\eta_c \Lambda),(\bar D \Xi_c')$ states. Most striking is the small width of about 1 MeV of the lower state. The upper state may be significantly broader due to a strong coupling to the $(\eta' \Lambda)$ state. The spectrum of crypto-exotic charm-zero states is completed with an isospin triplet state at 3.93 GeV and an isospin doublet state at 3.80 GeV. The dominant decay modes involve again the $\eta'$ meson.Comment: Talk presented at N*2005, 10 pages, 1 figur

A QM/MM equation-of-motion coupled-cluster approach for predicting semiconductor color-center structure and emission frequencies

Valence excitation spectra are computed for all deep-center silicon-vacancy defect types in 3C, 4H, and 6H silicon carbide (SiC) and comparisons are made with literature photoluminescence measurements. Nuclear geometries surrounding the defect centers are optimized within a Gaussian basis-set framework using many-body perturbation theory or density functional theory (DFT) methods, with computational expenses minimized by a QM/MM technique called SIMOMM. Vertical excitation energies are subsequently obtained by applying excitation-energy, electron-attached, and ionized equation-of-motion coupled-cluster (EOMCC) methods, where appropriate, as well as time-dependent (TD) DFT, to small models including only a few atoms adjacent to the defect center. We consider the relative quality of various EOMCC and TD-DFT methods for (i) energy-ordering potential ground states differing incrementally in charge and multiplicity, (ii) accurately reproducing experimentally measured photoluminescence peaks, and (iii) energy-ordering defects of different types occurring within a given polytype. The extensibility of this approach to transition-metal defects is also tested by applying it to silicon-substitutional chromium defects in SiC and comparing with measurements. It is demonstrated that, when used in conjunction with SIMOMM-optimized geometries, EOMCC-based methods can provide a reliable prediction of the ground-state charge and multiplicity, while also giving a quantitative description of the photoluminescence spectra, accurate to within 0.1 eV of measurement in all cases considered.Comment: 13 pages, 4 figures, 6 tables, 5 equations, 100 reference

Critical role of canonical transient receptor potential channel 7 in initiation of seizures

Status epilepticus (SE) is a life-threatening disease that has been recognized since antiquity but still causes over 50,000 deaths annually in the United States. The prevailing view on the pathophysiology of SE is that it is sustained by a loss of normal inhibitory mechanisms of neuronal activity. However, the early process leading to the initiation of SE is not well understood. Here, we show that, as seen in electroencephalograms, SE induced by the muscarinic agonist pilocarpine in mice is preceded by a specific increase in the gamma wave, and genetic ablation of canonical transient receptor potential channel (TRPC) 7 significantly reduces this pilocarpine-induced increase of gamma wave activity, preventing the occurrence of SE. At the cellular level, TRPC7 plays a critical role in the generation of spontaneous epileptiform burst firing in cornu ammonis (CA) 3 pyramidal neurons in brain slices. At the synaptic level, TRPC7 plays a significant role in the long-term potentiation at the CA3 recurrent collateral synapses and Schaffer collateral-CA1 synapses, but not at the mossy fiber-CA3 synapses. Taken together, our data suggest that epileptiform burst firing generated in the CA3 region by activity-dependent enhancement of recurrent collateral synapses may be an early event in the initiation process of SE and that TRPC7 plays a critical role in this cellular event. Our findings reveal that TRPC7 is intimately involved in the initiation of seizures both in vitro and in vivo. To our knowledge, this contribution to initiation of seizures is the first identified functional role for the TRPC7 ion channel.Fil: Phelan, K. D.. University of Arkansas for Medical Sciences; Estados UnidosFil: Shwe, U. T.. University of Arkansas for Medical Sciences; Estados UnidosFil: Abramowitz, J.. National Institute of Environmental Health Sciences; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Birnbaumer, Lutz. National Institute of Environmental Health Sciences; Estados UnidosFil: Zheng, F.. University of Arkansas for Medical Sciences; Estados Unido

Quark-mass dependence of baryon resonances

We study the quark-mass dependence of J^P = \frac12^- s-wave and J^P = \frac32^- d-wave baryon resonances. Parameter-free results are obtained in terms of the leading order chiral Lagrangian. In the 'heavy' SU(3) limit with m_\pi =m_K \simeq 500 MeV the s-wave resonances turn into bound states forming two octets plus a singlet representations of the SU(3) group. Similarly the d-wave resonances turn into bound states forming an octet and a decuplet in this limit. A contrasted result is obtained in the 'light' SU(3) limit with m_\pi =m_K \simeq 140 MeV for which no resonances exist.Comment: 8 pages, three figures, talk presented at HYP200

Dusty Sources at the Galactic Center: The N- and Q-band view with VISIR

We present mid-infrared N- and Q-band photometry of the Galactic Center from images obtained with the mid-infrared camera VISIR at the ESO VLT in May 2004. The high resolution and sensitivity possible with VISIR enables us to investigate a total of over 60 point-like sources, an unprecedented number for the Galactic Center at these wavelengths. Combining these data with previous results at shorter wavelengths (Viehmann et al. 2005) enables us to construct SEDs covering the H- to Q-band regions of the spectrum, i.e. 1.6 to 19.5 $\mu$m. We find that the SEDs of certain types of Galactic Center sources show characteristic features. We can clearly distinguish between luminous Northern Arm bow-shock sources, lower luminosity bow-shock sources, hot stars, and cool stars. This characterization may help clarify the status of presently unclassified sources.Comment: 18 pages, 4 figures, 1 table, accepted for publication in the Astrophysical Journa

The Infrared Extinction Law at Extreme Depth in a Dark Cloud Core

We combined sensitive near-infrared data obtained with ground-based imagers on the ESO NTT and VLT telescopes with space mid-infrared data acquired with the IRAC imager on the Spitzer Space Telescope to calculate the extinction law A_\lambda/A_K as a function of \lambda between 1.25 and 7.76 micron to an unprecedented depth in Barnard 59, a star forming, dense core located in the Pipe Nebula. The ratios A_\lambda/A_K were calculated from the slopes of the distributions of sources in color-color diagrams \lambda-K vs. H-K. The distributions in the color-color diagrams are fit well with single slopes to extinction levels of A_K ~ 7 (A_V ~ 59 mag). Consequently, there appears to be no significant variation of the extinction law with depth through the B59 line of sight. However, when slopes are translated into the relative extinction coefficients A_\lambda/A_K, we find an extinction law which departs from the simple extrapolation of the near-infrared power law extinction curve, and agrees more closely with a dust extinction model for a cloud with a total to selective absorption R_V=5.5 and a grain size distribution favoring larger grains than those in the diffuse ISM. Thus, the difference we observe could be possibly due to the effect of grain growth in denser regions. Finally, the slopes in our diagrams are somewhat less steep than those from the study of Indebetouw et al. (2005) for clouds with lower column densities, and this indicates that the extinction law between 3 and 8 micron might vary slightly as a function of environment.Comment: 22 pages manuscript, 4 figures (2 multipart), 1 tabl

A 1200-micron MAMBO survey of ELAISN2 and the Lockman Hole - I. Maps, sources and number counts

The definitive version is available at www.blackwell-synergy.com '.--Copyright Blackwell Publishing. DOI : 10.1111/j.1365-2966.2004.08235.xWe present a deep, new 1200μm survey of the ELAISN2 and Lockman Hole fields using the Max Planck Millimeter Bolometer array (MAMBO). The areas surveyed are 160 arcmin2 in ELAISN2 and 197 arcmin2 in the Lockman Hole, covering the entire SCUBA ‘8mJy Survey’. In total, 27 (44) sources have been detected at a significance 4.0 ( 3.5 ). The primary goals of the survey were to investigate the reliability of (sub)millimetre galaxy (SMG) samples, to analyse SMGs using flux ratios sensitive to redshift at z > 3, and to search for ‘SCUBA drop-outs’, i.e. galaxies at z >> 3. We present the 1200μm number counts and find evidence of a fall at bright flux levels. Employing parametric models for the evolution of the local 60μm IRAS luminosity function (LF), we are able to account simultaneously for the 1200 and 850μm counts, suggesting that the MAMBO and SCUBA sources trace the same underlying population of high-redshift, dust-enshrouded galaxies. From a nearest-neighbour clustering analysis we find tentative evidence that themost significantMAMBO sources come in pairs, typically separated by 23′′. Our MAMBO observations unambiguously confirm around half of the SCUBA sources. In a robust sub-sample of 13 SMGs detected by both MAMBO and SCUBA at a significance 3.5 , only one has no radio counterpart. Furthermore, the distribution of 850/1200μmflux density ratios for this sub-sample is consistent with the spectroscopic redshift distribution of radio-detected SMGs (Chapman et al. 2003). Finally, we have searched for evidence of a high-redshift tail of SMGs amongst the 18 MAMBO sources which are not detected by SCUBA. While we cannot rule out that some of them are SCUBA drop-outs at z >> 3, their overall 850-to-1200μm flux distribution is statistically indistinguishable from that of the 13 SMGS which were robustly identified by both MAMBO and SCUBA.Peer reviewe